The basic concept of the digital backend that I want to introduce to you today is Track. Track refers to the trace track, which, like row, can constrain the direction of the trace device. The signal line usually has to be on the track. The height of an std cell is usually expressed by metal2 track pitch. The commonly used std cell libraries are 7T / 9T / 12T, which are distinguished by track. 9T means that nine lines can be walked within the height range of an std cell, so generally speaking, the size of a 7T cell is the smallest, and the size of a 9T cell is slightly larger. big.
The colorful lines in the figure below are the track traces defined on each layer.
Usually we define the attributes of track in the technology lef of design, as shown in the figure below：
LAYER M1
TYPE ROUTING ;
DIRECTION VERTICAL ;
PITCH 0.090 0.064;
OFFSET 0.000 0.000;
MAXWIDTH 2 ;
WIDTH 0.032 ;
In the definition of M1 layer above, TYPE ROUTING means that this is a routing layer. We have other types including Implant, Masterslice, etc.
The direction represents the direction of the metal prefer routing of this layer. It is worth noting here that each layer of track will be divided into pref track and non-pref track. The pref track is the mainstream routing direction on this layer, and the remaining non-pref track is the non-mainstream direction. Therefore, the mainstream routing direction in the above example is vertical (vertical), and the non-mainstream is horizontal (honrizontal). usually. The wire that takes the non-pref track will be wider, which will take up more winding resources. Therefore, it is generally not recommended to use non-pref track. Especially in the design of advanced processes, winding resources are extremely tight, and non-pref track is generally rarely used.
PITCH IS the SPACING BETWEEN EACH track. In the above example, the vertical spacing is 0.09 and the horizontal spacing is 0.064.
OFFSET is the distance from the starting point of the first track
WIDTH represents the default width of the wire on this layer, and MAXWIDTH represents the maximum width that cannot be exceeded.
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